digestion

1

Animal nutrition

2

The modes of nutrition

Nutrition refers to all the processes by which organisms obtain and use the nutrients required for maintaining life.

Nutrients are substances which organisms need for releasing energy, for growth and repair, and to sustain all life processes

The different ways that organisms obtain and use nutrients are called the modes of nutrition.

3

Homeostasis - metabolism

All of these nutritional modes are found among prokaryotes!Eukaryotes are not as diverse in their nutritional modes.

Nutrition ModeEnergy Source

Carbon Source

Photoautotroph Light CO2

ChemoautotrophInorganic

chemCO2

Photoheterotroph LightOrganic chem

ChemoheterotrophOrganic chem

Organic chem

5

Photoautotrophs - photosynthesis Ancient pathway, but not universal Cyanobacteria, Algae, Plants

light

CO2 + H2O O2 + CH2Ochlorophyll

Purple-sulfur bacterialight

CO2 + H2S Ss + CH2Ochlorophyll

6

Chemoautotrophs 1. Nitrifying bacteria which derive energy

by oxidizing ammonia into nitrates. Eg: Nitrosomonas, Nitrobacter.

2. Sulphur bacteria which derive energy by oxidising hydrogen sulphide to sulphur. Eg: Thiobacillus, Beggiatoa.

3. Iron Bacteria which derive energy by oxidising ferrous ions into ferric form. Eg: Ferrobacillus, Gallionella.

7

http

://m

icro

bew

iki.k

enyo

n.ed

u/im

ages

/thum

b/8/

89/Z

drs0

232.

jpg/

350p

x-Z

drs0

232.

jpg

Nitrosomonas - internal membranes use NH4

+ electrons in an ETS to produce ATP ATP and protons used to reduce CO2 to CH2O

8

Rhizobium needs anaerobic conditions to convert N2 into NH4+

Legumes produce heme based molecules and rapid respiration to eliminate oxygen from root nodules that house the bacterium“symbiosis”

http

://w

ww

.inte

ret-

gene

ral.i

nfo/

IMG

/rhi

zobi

um-n

odul

e-1.

jpg

9

Photoheterotrophs - strange

Bacteria: Rhodospirillum, Rhodomicrobium Light

C2H4O2- 2 CH2O

10

Chemoheterotrophs - common!

Escherichia coli and most eukaryotes…even plants!

CH2O + O2 CO2 + H2O + ATP

Carbohydrate, etc. provides boththe energy source

andthe carbon source

11

Chemoheterotrophy Aerobic Respiration

Glycolysis carbohydrate to pyruvate (in cytosol!) Citric Acid Cycle pyruvate to carbon dioxide (in cytosol or

matrix) Electron Transport and Oxidative Phosphorylation (in

mesosomes or cristae)

CH2O + O2 CO2 + H2O Anaerobic Fermentation

Glycolysis to pyruvate (in cytosol) Fermentive step(s) to return NAD+ to glycolysis (in cytosol)

C6H12O6 C3H3O3- C2H5OH + CO2

C6H12O6 C3H3O3- H3CCHOHCOO-

12

Autotrophic nutrition

Chemoheterotrophic nutrition

Holozoic nutrition

Parasitic nutrition

Saprophytic nutrition

Herbivores

Carnivores

Omnivores

13

Heterotrophic nutrition consumes complex organic food material which originates from autotrophic organisms.

There are several forms of heterotrophic nutrition:

1. Holozoic nutrition 2. Saprophytic nutrition 3. Parasitic nutrition 4. Mutualism 5. Commensalism

14

Intracellular Digestion Lysosomes fuse with food vacuoles Digestion occurs within the cell Sponges only digest food

intracellularly

15

Extracellular Digestion Breakdown of food outside of cells Gastrovascular cavities serve as

digestive sacs Enzymes in cavity begin extracellular

digestion After absorption, digestion is completed

intracellularly Animals with alimentary canals organize

digestion in stepwise fashion

16

Saprophytes

17

Saprophytes saprophytes obtain food from dead

organic matter, e.g. bacteria and fungi

Mucor is a bread mould (fungus) which depends on bread for food; hyphae: filaments mycelium: colony of filaments

18

Nutrition - hyphae (rhizoid) go into bread; produce digestive enzymes to break

down complex organic substances in bread into simple soluble compounds for absorption

Extracellular digestion: digestion outside the cell

Importance of saprophytism: dead organisms are broken down to

recycle materials

19

rostellumhook

sucker

immature proglottis

Tapeworm1. Structure of a tapeworm flat, long, ribbon like, with many (1000)

segments head with hooks & suckers for attachment

onto the host’s intestinal wall each segment contains both male & female

reproductive organs (bisexual) for self-fertilization

2. Life cycle Primary host - man; Secondary host - pig, for dispersal & infection

21

3. Adaptation of tapeworm to the parasitic mode of life in the ileum

hooks & suckers for attaching itself onto the intestinal wall of host

reproductive organs are well developed;

bisexual for self-fertilization numerous eggs are produced to increase the chances of survival of the species

22

no digestive system is needed; absorption of digested food by

diffusion through the body surface which is long & flattened to increase the surface area for absorption of digested food

can undergo anaerobic (no O2) respiration in the intestine

body is covered by a thick cuticle and secretes anti-enzymes to protect itself against the digestive juice of host

23

4. Effect on host host loses weight & becomes weak because

tapeworm absorbs his digested food hooks & suckers damage the intestinal wall of

host

5. Means to get rid of tapeworm take in drugs pork should be inspected by government

before selling; pork should be thoroughly cooked before

eating good sewage system so that pigs do not get

in contact with human faeces

2007 Paper II Q.5 (a)

24

25

Mineral Nutrition in plants

Plants need certain nutrients. A deficiency in any one of them will cause the plant to be impaired in growth and other functions.

1. C, H, and O are the most abundant elements in plants. They are obtained from water from the soil and CO2 in the air (of course).

2. Other essential elements have historically been grouped as macronutrients and micronutrients. a. Macronutrients are needed in somewhat higher amounts, and make up at least 0.1% of the dry weight of most plants, although this can vary among plants and among tissues within plants.b. Elements needed in smaller amounts are known as micronutrients.

28

Advantages in hydroponics

no weeds, no pests.

The necessary growth elements are readily available.

Use less space

Possible to automate

can grow crops in greenhouse

allow precise water and nutrient application

2007 Paper II Q.5 (a)

29

30

3. Holozoic nutrition – involves the consumption of complex (solid) food which is broken down inside the organism into simple molecules which are then absorbed,

e.g. most animals

31

20 primary teeth (deciduous (“falling off”) teeth) which appear during embryonic development Are the temporary teeth of primary dentition Are also known as primary teeth, milk teeth, baby

teeth 32 teeth of adult secondary dentition, or

permanent dentition

Eruption of teeth

32

Teeth

Figure 24.8a, b

33

Primary and Secondary Teeth

A). Primary teeth, with the age of eruption given in months. (B). The adult teeth, with the age of eruption given in years.

35

Carnivorous adaptations of mammalsFood is chiefly meat which is a more

'nutritional' than plant food. Adaptations concern modifications to the jaw & its dentition:

1. Incisors are sharp and are used for nipping & biting

36

2. Canines are long & pointed; used for killing prey and tearing flesh from body3. Carnassial teeth are particularly large for crushing

bones4. Teeth of upper jaw tend to overlap those of the

lower jaw for slicing meat like two blades of a pair of scissors

37

5. Jaw muscles are well developed & powerful to grip prey firmly & crushing bones

6. No lateral jaw movement which might lead to dislocation of the jaw

7. Vertical movement of the jaw is large to allow a wide gap for capturing & killing prey

8. The alimentary canal is short, i.e. meat is relatively easy to be digested

38

Adaptations to particular dietsHerbivorous adaptations of mammals, e.g.

deer1. A horny pad replaces the upper incisors

& canines 2. Diastema - a gap to separate newly

nibbled food from those chewing at the back

Skull of deer

39

Dental formula of a sheep : 0033 31233. Cheek teeth with ridged surfaces

because of differential wearing of enamel and dentine

40

4. Jaws can move vertically & laterally - for more efficient grinding by teeth5. Teeth have open roots - teeth grow continuously throughout life to

replace wearing by constant grinding activity

6. Stomach is divided into a number of chambers with micro-organisms to secreted cellulase for the digestion of cellulose (ruminants). Regurgitation of food from stomach to mouth before passing into the remaining stomach compartments

7. The alimentary canal is relatively long because the digestion of plant material is difficult

41

Comparison of herbivorous and carnivorous adaptations in mammals

Herbivores Carnivores Incisors sharp, chisel-shaped for cutting or gnawing (bite until off)

Incisors sharp, sometimes pointed, for nipping (to hold) & biting

Upper incisors sometimes absent

…never absent

Canines, if present, small & incisor-like

Canines long & pointed for piercing & tearing

Diastema present …absent

Molars & premolars flattened with ridges of enamel for grinding food

…have pointed cusps for shearing food

42


Herbivores Carnivores

Carnassial teeth absent Carnassial teeth: last upper premolars & first molars

Open pulp cavity for continuous teeth growth to compensate for wearing

Closed cavity with no growth when grow to full size

Teeth of upper jaw meet those of lower jaw end on to allow grinding of food

Teeth of upper jaw slide past outside of lower jaw: shear food

Lateral movement of lower jaw aids grinding of food

No such movement to avoid dislocation of the lower jaw

43


Herbivores Carnivores

Jaw muscles relatively small

….relatively large

Less well developed processes for muscle attachment

Well developed ….

Specialized stomach/caecum & appendix to accommodate symbiotic cellulose digesting micro-organisms

No such adaptation;Caecum & appendix small

Relatively long alimentary canal

…short alimentary canal

44

Five stages of Food Processing

1. Ingestion2. Digestion (enzymatic hydrolysis)3. Absorption4. Assimiation5. Elimination

46

Principles of Digestion Mechanical breakdown of food has

the effect of giving the food a large surface area which aids later digestion.

The food must be made small enough to pass through cell membranes. Thus chemical digestion with the aid of enzymes occurs.

amylase - breaks down starch into maltose

47

Mucosa lines digestive tract (mucous epithelium) Moistened by glandular secretions Lamina propria and epithelium form mucosa

Submucosa Layer of dense irregular connective tissue

Muscularis externa Smooth muscle arranged in circular and longitudinal layersSystem (ENS)

Serosa Along most portions of the digestive tract inside the peritoneal cavity, the

muscularis externa is covered by a serous membrane known as the serosa

Histological organization of the digestive tract

48

The Structure of the Digestive Tract

http://visualhistology.net/products/atlas/VHA_Chpt13_The_Alimentary_Canal.html

49

Mouth

Mechanical digestion: the act of chewing Carbohydrate digestion begins here Saliva moistens food and contains the

enzyme Salivary Amylase – breaks down complex carbs into simple sugars

Chemical Digestion: enzymes breaking down carbohydrates

Ball of moistened, partially digested food, known as the “BOLUS”, moves into the esophagus

50

Swallowing and peristalsis- pharynx leads to both trachea &

oesophagus- when swallowing food, epiglottis closes

entrance to trachea to prevent food going into lungs

52

Carries solids and liquids from the pharynx to the stomach Passes through esophageal hiatus in diaphragm

The wall of the esophagus contains mucosal, submucosal, and muscularis layers

The esophagus

53

Distinctive features of the esophageal wall include Nonkeratinized, stratified squamous epithelium Folded mucosa and submucosa

• Mucous secretions by esophageal glands A muscularis with both smooth and skeletal

muscle portions Lacks serosa

• Anchored by an adventitia (superficial layer of connective tissue surrounding an internal organ; fibers are continuous with those of surrounding tissues, providing support and stabilization)

Histology of the esophagus

54

The Esophagus

A). Transverse cross section through the esophagus. (B). The esophageal mucosa (C). A color enhanced SEM of the transition between the esophageal and gastric mucosae at the lower esophageal sphincter.

55

Peristalsis - longitudinal & circular muscles contract & relax alternately to drive food down oesophagus, small intestine, large intestine & out of the anus as faeces

57

Stomach contractions: blend food and propel forward

Stomach Contraction

Direction: from lower esophageal sphincter to pyloric sphincter

Chyme: result of mixing, affects hormone secretions regulating peristalsis and emptying of stomach

58Figure 14.7Slide 14.9ACopyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Structure of the Stomach Wall

62

Lining of ileum

TS of ileum showing villi

64

Duodenum Brunner's glands secrete mucus and

sodium hydrogen carbonate

Enzymes are produced by the breakdown of cells at the tips of the villi

1. Mucus – lubricate and prevent autolysis 2. Mineral salts (NaHCO3) - produced by the Brunner’s glands to

neutralize the acid chyme and provide a suitable pH for intestinal enzymes

65

Bile juice A complex green fluid produced by the liver,

stored in the gall bladder, It contains no chemical enzymes but two

important substances for digestion: 1. Sodium hydrogen carbonate - help to neutralize the acid chyme from the

stomach and so create a more neutral pH for the enzymes of the small intestine

2. Bile salts - They emulsify fats into minute droplets - This is a physical digestion which increases

the surface area for pancreatic lipase to act on

67

Large Intestine Unabsorbed material moves through large

intestine, where water and salt are absorbed

This removal of liquid forms solid-like feces

Feces is stored in the rectum Feces is removed from the body, via the

anus, by the process of ELIMINATION

69

Cecum

Lies below junction with small intestine

Contains appendix

Colon

Includes ascending colon, transverse colon, descending colon

Rectum

Last 20 cm of the large intestine

Anus

Where defecation (expulsion of feces) occurs

Obligate anaerobic (die in presence of oxygen) bacteria inhabit colonBreak down indigestible material and produce vitamins & other molecules used by our bodies

70

http://www.youtube.com/watch?v=IRiwXMeKoGk&feature=grec_index

71

Chemistry of Digestion Digestion is defined as the

breakdown of nutrients We consume: Proteins Carbohydrates Fats These are broken down into their

simplest forms

72

Overview

74

Salivary amylase- digest starch into maltose Pancreatic amylase Carbohydrases in small intestine - consisting of maltase, lactase, and

sucrase, etc., to complete the digestion of sugars into simple sugars

Slide 14.9BCopyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Digestion of carbohydrates

75

Gastric juice: specific cells secrete

Hydrochloric acid (from chief cells): produces a pH of about 2, breaks down large bits of food

Intrinsic factor; made by same cells making acid, needed to absorb Vitamin B12

Mucus: protects stomach lining from acid Pepsinogen (from Parietal Cells) : with

acid, begins protein breakdown Rennin: milk coagulation

Slide 14.9BCopyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Digestion of protein – stomach

76

endopeptidases – break down peptide bonds in the middle of peptides

peptidases – break down peptides into amino acids

77

Proteases (from pancreas)trypsinogen trypsin

enterokinase (from intestine)

Proteins peptides trypsin

Chemotrypsinogen chemotrypsintrypsin

Proteins peptideschemotrypsin

Small peptides amino acidscarboxypeptidase

78

Endopeptidases (first) hydrolyse peptide bonds at points along the protein

Carboxypeptidase liberates terminal amino acids

COOH NH2

Exopeptidases acts on terminal amino acids

Aminopeptidase breaks terminal amino acids with –NH2 group

79

From instestinal juice

exopeptidases – break down peptide bonds on terminal amino acids aminopeptidases – break down amino

acids with a free amino (-NH2) group

Carboxypeptidase liberates terminal amino acids with free COOH

2002 Paper II B Q.4 (b) maternal digestion: protease breaks down

proteins to amino acids (1) / peptides, in stomach and small intestine (1)

absorbed into the maternal blood stream at the ileum (1)

a.a. carried via veins to hearts, then along artery to uterine wall (1)

a.a. diffuse across the *placenta into foetal blood circulation (1)

80

81

Digestion of lipid

Bile salts - They emulsify fats into minute

droplets - This is a physical digestion which

increases the surface area for pancreatic lipase to act on

Lipase -hydrolyses fats into fatty acids

and glycerol

83

Digestion of nucleic acid

Nuclease -changes nucleic acids into

nucleotides

Other substances

Many substances in the diet are composed of small molecules that need little or no digestion. These include sugars, mineral ions, vitamins and water. These are absorbed by different transport mechanisms: • Cholesterol and the fat-soluble vitamins (A, D, E, K) are

absorbed into the epithelial cells of the ileum by lipid diffusion

• Mineral ions and water-soluble vitamins are absorbed by passive transport in the ileum

• Dietary monosaccharides are absorbed by active transport in the ileum Water is absorbed by osmosis in the ileum and colon.

84

89

Regulation of Digestion

Regulation dependent on volume and content of food

Neural and hormonal mechanisms coordinate glands

Nervous system: stretch receptors in stomach

GI activity stimulated by parasympathetic innervation

Inhibited by sympathetic innervation

90

Hormones:Stomach

• Gastrin: stimulates release of gastric juice

Duodenum• Secretin: stimulates pancreas to secrete water and bicarbonate• Cholecystokinin (CCK): signal the smooth muscle of the gall

bladder to contract• Pancreozymin ： signals pancreas to secrete digestive enzymes

Coordination secretion and absorption

91

stom ach

gall bladder

pancreas

duodenum

stom ach

gall bladder

food (lip id )

pancreas

duodenum

stom ach

gall bladder

food (lip id )ga str ic ju ice

pancreas

duodenum

Secretin

stom ach

gall bladder

food (lip id )ga str ic ju icepa ncrea tic flu id (b ica rbon a te)

pancreas

duodenum

CCK

CCK

stom ach

gall bladder

food (lip id )ga str ic ju icepa ncrea tic flu id (b ica rbon a te)pa ncrea tic enzym e (lipa se )

pancreas

duodenum

stom ach

gall bladder

food (lip id )ga str ic ju icepa ncrea tic flu id (b ica rbon a te)

b ile ju icepa ncrea tic enzym e (lipa se )

pancreas

duodenum

92

The Activities of Major Digestive Tract Hormones

93

Absorption Very little is absorbed from stomach and large

intestine Most absorption is from SI Large SA of microvilli enhance absorption cap

acity Capillaries from villi converge into hepatic

portal vein Cecum is an extension of LI E. coli live in LI and generate gas and vitamins Water is reabsorbed from SI and LI Diarrhea and constipation result from

abnormal water reabsorption

94

Absorption of Proteins and Carbohydrates

95

Absorption of Fats

96

Absorption of Nutrients

Proteins and carbohydrates: active transport

Lipids: broken down and reassembled

Water: osmosis

Vitamins and minerals: assorted means

97

The Intestinal Wall

D). Internal structures of a single villus, showing the capillary and lymphatic suppliesE). A villus in sectional view (LM X 252)

The structure of the small intestine (ileum) in relation to its functions

The millions of finger-like villi cover the entire surface of the intestinal lining. The villi are greatly folded to increase the surface area for absorption. The wall of the villi are thin (with only one layer of epithelial cells) and this

permit the food to diffuse through easily. The epithelial cells lining the villi have cylindrical projections called brush

border micro-villi. These further increase the surface area of absorption. The villi contain blood capillaries to absorb glucose and amino acids through

the hepatic portal system to the liver. The villi contain lacteals to absorb fatty acids and glycerol. Glandular cells in epithelial lining which secrete digestive enzymes for

digestion of food molecules as they pass through. Circular and longitudinal muscles involved with peristalsis. They mix the

digestive juices with chyme so promoting hydrolysis of food by the enzymes. Mucus secretion which protects epithelium.

99

100

The Intestinal Wall

Crypt of Lieberkuhn• Cells secrete proteins, fluids, electrolytes– Paneth cells – secrete proteins– Goblet cells – secrete mucus• These cells also serve as protectivebarrier against pathogens• Epithelial cells undergo mitosis and travelto tips of villi the sloghed off• Intestinal cell turnover is rapid ~ 3-5 days

Absorption in large intestine

101

102

Nutrients:Utilized or Stored Until Needed

2006 Paper IIB Q.8

103

2006 Paper IIB Q.8

104

105

Liver Largest gland in the body

Has two lobes—large right and small left

Contains approximately 100,000 lobules that serve as structural and functional units

Triads, consisting of three structures, located between the lobules

Bile duct—takes bile away from liver

Hepatic artery—brings O2-rich blood to liver

Hepatic portal vein—transports nutrients from intestines

The central veins of lobules enter a hepatic vein

106

The Liver - an organ for digestion and homeostasis

107

Blood system associated with the liver

108

The Structure of The Liver

- Blood is drained into the liver by 2 vessels: the hepatic artery and the hepatic portal vein- Blood is drained away from the liver by the hepatic vein

112

- Branches of the hepatic artery & heptic portal vein combine within the liver to form common venules which lead into a series of channels called sinusoids.

Sinusoids are lined with liver cells (hepatocytes) and drains into a branch of the hepatic vein called the central vein.

- Between the hepatocytes are fine tubes called canaliculi in which bile is secreted.

The canaliculi combine to form bile ducts which drain into the gall bladder.

- The functional unit of the liver is the acinus. In the sinusoids materials are exchanged

between the hepatocytes and blood.

113

Structures of hepatocytes for exchange of materials with high metabolic rate:

microvilli, large nucleus, many mitochondria, lysosomes and glycogen granules.The canaliculi are also lined with

microvilli to remove bile from the hepatocytes by active transport.

114

- Sinusoids are lined with endothelial cells with specialized Kupffer cells of the reticulo-endothelial system for ingesting any foreign materials and damaged, worn out RBCs.

Bilirubin is produced as a by-product & excreted in the bile.

115

Functions of The LiverThe liver has about 500 individual functions. They are grouped as below:1.Carbohydrate metabolism - action of insulin & glucagon by inlets of

Langerhans2.Lipid metabolism - lipids are broken down or transported to

storage areas - excess carbohydrates lipid - regulate cholesterol level; atherosclerosis

& gall stones

116

3. Protein metabolism - deamination - transamination to synthesize non-

essential amino acids4. Synthesis of plasma proteins, e.g. clotting factors: prothrombin &

fibrinogen5.Production of bile:

bilirubin + bile salts + NaCl + HCO3-

6.Storage of vitamins, especially fat soluble vitamins A, D, E, K

7.Storage of minerals, e.g. Fe, K, Cu & Zn

117

8. Formation & breakdown of RBCs

- foetal liver produces RBCs - adult liver breaks down aged RBCs9. Storage of blood - about 1500 cm3 of blood can be stored10.Hormone breakdown, e.g. testosterone, insulin etc11.Detoxification - Kupffer cells ingest foreign materials - hepatocytes convert toxic chemicals into harmless

forms12. Production of heat - when body temperature falls - triggered by the hypothalamus, is in response to

adrenaline, thyroxine & nervous stimulus

digestion

Documents

addison wesley

lower esophageal

terminal amino

alimentary

digestive

amino acids

peptide bonds

lower jaw